Abstract Hematopoietic stem cells and progenitors (HSPCs) are a rare population of self-renewing bone marrow (BM) cells that can generate all mature lineage blood cells for the lifespan of an organism. In adults, quiescent HSPCs reside within a hypoxic bone marrow niche (1-4% O2 physiologic hypoxia) and are capable of rapidly entering the cell cycle and differentiate to produce leukocytes in response to an invading pathogen. The mentor?s lab uncovered that resolution of inflammation is governed by spatial and temporal production of novel mediators and elucidated the specialized pro-resolving mediators (SPMs), a superfamily of autacoids that includes lipoxins (LX), resolvins (Rv), protectins (PD), and maresins (MaR). SPM biosynthesis structures and functions were established in the mentor?s lab and confirmed by others. SPMs are sub-nanomolar potent, stereoselective agonists that promote microbial clearance and containment, while enhancing host survival by accelerating host resolution mechanisms. This proposal is based on new findings from work in progress; we identified, using state- of-the-art metabololipidomics profiling, a specific SPM cluster in HSPC under physiologic hypoxia, which includes Resolvin D1 (RvD1), Resolvin D4 (RvD4), Resolvin E1 (RvE1), Maresin 1 (MaR1) and Lipoxin B4 (LXB4). Also, we recently identified a new SPM, Resolvin E4 (RvE4), in healthy human bone marrow. Tissues that experience physiologic hypoxic niches, such as BM, have high amounts of SPMs through undefined mechanisms. Thus, we propose to rigorously test the following hypothesis: In physiologic hypoxia, specialized pro-resolving mediators (SPMs) produced in BM are essential for regulating HSPC responses de novo and/or during infection at distal sites of invasion, as well as maintaining BM homeostasis. The following aims are proposed by using state-of-the-art omics platforms e.g., metabolipidomics (LC-MS/MS), mass cytometry (CyTOF) and single cell RNA sequencing (sc-RNA-seq) in murine and human HSPCs to: 1) determine the impact of physiologic hypoxia on endogenous novel SPM production in BM niche (K99), and 2) establish the regulation of HSPC differentiation and responses to infection by the SPM cluster, specifically RvD1, RvD4, MaR1 and the novel RvE4 (K99/R00). The K99 mentored phase will take place at Brigham and Women?s Hospital and Harvard Medical School under the mentorship of two internationally recognized scientists, Professor Charles N. Serhan, the leader in the structural elucidation of SPMs and their functions and Professor Leonardo Zon, the leader on hematopoiesis. Dr. Libreros will be further advised by a scientific committee/collaborator covering different aspects of the research proposal: Dr. Matthew Spite, Dr. Mark Perrella, and Professor David Scadden. The goal of this proposal is to provide a comprehensive scientific and career development plan for the applicant with the required skills to transition to an independent faculty position (R00). Results from these studies will yield fundamentally new insights into the functions of SPMs and novel pro-resolving pathways in HSPC biology. These discoveries can help develop novel treatments for hematological disorders and provide a basic understanding of how bone marrow supports resolution programs during infections.